1. Field of the Invention
The present invention relates to a power zoom lens including an automatic focusing device and a power zooming device, and a camera system having such a power zoom lens.
This application is related to the commonly assigned applications U.S. Ser. No. 07/410,880, 07/652,038, 07/407424, 07/414477, 07/41478, 07/670733, 07/406523, and 07/414476, the disclosures of which are expressly incorporated by reference herein.
2. Description of Related Art
There are various known lens shutter type cameras having automatic focusing devices and power zoom lenses with zoom motors. In an automatic focusing device in a single lens reflex camera, a focusing lens unit is moved by an AF motor in accordance with a detection signal outputted from a focus detecting device.
However, a single lens reflex camera having a power zoom lens has not been realized, since the provision of the power zoom lens not only complicates the mechanical construction of the camera body and the electrical connection to the camera body, but also makes it difficult to realize a simple interchangeable mechanism which is capable of connecting a conventional camera body to interchangeable lenses.
Furthermore, in a conventional single lens reflex camera, the drive of the AF motor is controlled by a CPU (microcomputer) provided in the camera body. It is also known to provide the AF motor in a taking lens, wherein electrical drive power is supplied to the AF motor by a battery provided in the camera body (e.g., Japanese Kokoku No. HEI 4-1554).
In this known single lens reflex camera, the power needed to drive the AF motor provided in the taking lens and the power needed to actuate a lens control circuit to control the AF motor are supplied to the taking lens from the camera body through common electrical terminals. Accordingly, if power cannot be appropriately supplied for some reason, for example, if there is a problem with the AF motor, the lens control circuit will not operate properly. If this occurs, the microcomputer provided in the camera body will cut the power supply to the taking lens.
The fact that an abnormal operation is occurring can be detected. However, it is impossible to identify the source of the trouble (e.g., the AF motor or lens control circuit) or the exact cause of the trouble (e.g., failure of electrical connection). Furthermore, once trouble occurs, the power supply to both the AF motor and the lens control circuit is cut, even if, for example, the control circuit normally works.